SOLA
Online ISSN : 1349-6476
ISSN-L : 1349-6476
Volume 15
Showing 1-49 articles out of 49 articles from the selected issue
Editorial
  • Tetsuya Takemi
    2019 Volume 15 Pages i-ii
    Published: 2019
    Released: January 09, 2019
    JOURNALS FREE ACCESS
    Supplementary material
    Scientific Online Letters on the Atmosphere (SOLA) has been a fully Open Access journal under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License (http://creativecommons.org/ license/by/4.0) since 2018. Since the establishment in 2005, SOLA has been pursuing rapid review cycle and rapid publication to disseminate scientific findings and knowledge in meteorology, atmospheric sciences, and the related fields. This goal is very challenging, but because of this goal, the number of papers submitted from the international community is increasing year by year.
    Last year, the Meteorological Society of Japan (MSJ) launched a new award, the Matsuno Award (MSJ 2017), to recognize the excellence in the presentation by graduate students at the MSJ meetings. SOLA will waive the Article Processing Charge for the papers authored by the recipients of the Matsuno Award. The papers authored by the recipients of the first Matsuno Award were published in SOLA (Yoshida and Takemi 2018; Yamamoto and Ishikawa 2018). In addition, SOLA is continuing to give The SOLA Award to outstanding paper(s) published each year. The Award winning paper in 2018 is Miura (2017) and Goto et al. (2017). The SOLA Award in 2018 will be announced shortly.
    In June 2018, the new Editorial Committee of SOLA has started and welcomed new members not only from Japan but also from the international community. SOLA welcomes submission from the international community in meteorology, atmospheric sciences, and the related fields.
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  • Tetsuya Takemi
    2019 Volume 15 Pages iii
    Published: 2019
    Released: February 01, 2019
    JOURNALS FREE ACCESS
    The Editorial Committee of Scientific Online Letters on the Atmosphere (SOLA) gives The SOLA Award to outstanding paper(s) published each year. I am pleased to announce that The SOLA Award in 2018 is going to be presented to the paper by Dr. Kosuke Ito et al., entitled with “Analysis and forecast using dropsonde data from the inner-core region of Tropical Cyclone Lan (2017) obtained during the first aircraft missions of T-PARCII” (Ito et al. 2018).
    Importance of dropsonde observations in the analysis and forecast of tropical cyclones (TCs) is well known, and such observations were operationally performed for the Atlantic hurricane. After the termination of the operational dropsonde observations in late 1980s, Dvorak technique has been used to estimate the intensity of TCs. However, uncertainties of Dvorak technique have been discussed for a long time, and dropsonde observations are essentially important for the precise information on TCs. The authors conducted dropsonde observations from an aircraft for TC Lan (2017) and, by assimilating the observed data, performed forecast experiments of the TC. They demonstrated potentially a positive impact of the dropsonde observations on the analysis and forecast of the TC. This study has demonstrated the importance of the dropsonde observations for TCs and is expected to enhance further studies investigations on the improvement of the analysis and forecast of TCs.
    Therefore, the Editorial Committee of SOLA highly evaluates the excellence of the paper.
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Article
  • Long Trinh-Tuan, Jun Matsumoto, Fredolin T. Tangang, Liew Juneng, Faye ...
    2019 Volume 15 Pages 1-6
    Published: 2019
    Released: January 19, 2019
    [Advance publication] Released: December 14, 2018
    JOURNALS FREE ACCESS
    Supplementary material

    The Quantile Mapping (QM) bias correction (BC) technique was applied for the first time to address biases in the simulated precipitation over Vietnam from the Regional Climate Model (RegCM) driven by five Coupled Model Intercomparison Project Phase 5 (CMIP5) Global Climate Model (GCM) products. The QM process was implemented for the period 1986-2005, and subsequently applied to the mid-future period 2046-2065 under both Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. Comparison with the original model outputs during the independent validation period shows a large bias reduction from 45% to 3% over Vietnam and significant improvements in representing precipitation indices (PI) after applying the QM technique. Moreover, the ensemble average of the BC products generally performed better than an individual BC member in capturing the spatial distribution of the PIs. A drier condition with a longer rainfall break, and shorter consecutive rainfall events are anticipated over Northern and Central Vietnam during their respective wet seasons in the mid-future. Furthermore, this study showed that the QM method minimally modified the future changes in PIs over most of Vietnam; thus, these corrected projections could be used in climate impacts and adaptation studies.

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  • Takumi Honda, Shohei Takino, Takemasa Miyoshi
    2019 Volume 15 Pages 7-11
    Published: 2019
    Released: January 19, 2019
    [Advance publication] Released: December 18, 2018
    JOURNALS FREE ACCESS

    Tropical cyclones (TCs) and associated heavy precipitation have large impacts in Japan. This study aims to find how data assimilation (DA) of every-10-minute all-sky Himawari-8 radiances could improve the quantitative precipitation forecast (QPF) for TC cases. As the first step, this study performs a single case study of Typhoon Malakas (2016) using a regional atmospheric model from the Scalable Computing for Advanced Library and Environment (SCALE) coupled with the local ensemble Kalman filter (LETKF). The results show that the all-sky Himawari-8 radiance DA at 6-km resolution improves the representation of Malakas and may provide more accurate deterministic and probabilistic precipitation forecasts if the horizontal localization scale is chosen appropriately.

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  • Akifumi Nishi, Hiroyuki Kusaka
    2019 Volume 15 Pages 12-16
    Published: 2019
    Released: February 05, 2019
    [Advance publication] Released: January 03, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study uses a numerical model to examine how a convex feature and a gap feature in a mountain range affect the leeward wind field. In the “convexity case”, the mountain ridge has a convex feature (viewed from above). In the “gap case”, the mountain ridge has a gap. The results show that both cases have local winds at the surface exceeding 8 m s−1, and both have similar spatial flow-patterns. However, the momentum budgets at the strong-wind regions differ between the cases. In the convexity case, the downdrafts are important in the momentum balance, whereas in the gap case, both the downdrafts and the pressure-gradient force are important. Thus, although their spatial patterns of surface wind are similar to each other, their mechanisms for producing a strong local wind differ.

    Sensitivity experiments of Frm show that strong-wind appears in both the convexity and gap cases when Frm is between 0.42 and 1.04. In contrast, when Frm is 0.21, strong winds only appear in the gap case because the flow can go around the gap. When Frm exceeds 1.25, strong surface winds appear in the entire leeward plain.

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  • Akifumi Nishi, Hiroyuki Kusaka
    2019 Volume 15 Pages 17-21
    Published: 2019
    Released: February 05, 2019
    [Advance publication] Released: January 15, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    In this study, we use observational data and numerical models to reveal whether foehn wind affects the record-breaking high-temperature event (41.1°C) at Kumagaya on July 23, 2018. On this day, the weather conditions at Kumagaya satisfied the conditions described in Takane et al. (2014) for a likely extreme high temperature (EHT) day: a “whale-tail” pressure pattern, no precipitation for 6 days, a high potential temperature at 850 hPa, and northerly surface winds. Our back-trajectory analysis shows that the air parcels came to Kumagaya from heights up to 3.0 km above sea level over the Sea of Japan. The Lagrangian energy budget analysis shows that adiabatic heating accounts for about 87.5% of the increase of the thermal energy given to the air parcel, with the rest from diabatic heating. The diabatic heating is caused by heating associated with surface sensible heat flux and the mixing by turbulent diffusion. The adiabatic and diabatic heating are calculated to have raised the temperature of air parcel by 14 and 2.0 K, respectively, for this EHT event. We conclude that the dynamic foehn effect and diabatic heating from the surface, together with mixing in the atmospheric boundary layer, affected the formation of this EHT event.

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  • Tetsuya Takemi, Toshiya Yoshida, Shota Yamasaki, Kentaro Hase
    2019 Volume 15 Pages 22-27
    Published: 2019
    Released: February 06, 2019
    [Advance publication] Released: January 16, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    An intense tropical cyclone, Typhoon Jebi (2018), landed the central part of Japan and caused severe damages. Quantitative assessment of strong winds in urban districts under typhoon conditions is important to understand the underlying risks. As a preliminary study, we investigate the influences of densely built urban environments on the occurrence of wind gusts in an urban district of Osaka City during Typhoon Jebi by merging mesoscale meteorological and building-resolving large-eddy simulations (LES). With the successful reproduction of the track and intensity of the typhoon in meteorological simulations, the simulated winds at the boundary-layer top of the LES model are used to quantitatively estimate the wind gusts in the urban district. The maximum wind gust in the analysis area of Osaka was estimated as 60-70 m s−1, which is comparable to the wind speed at the height of about 300 m.

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  • Truong Van Thinh, Phan Cao Duong, Kenlo Nishida Nasahara, Takeo Tadono
    2019 Volume 15 Pages 28-31
    Published: 2019
    Released: February 11, 2019
    [Advance publication] Released: January 24, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    A land use/land cover map is an important input for different applications. However, the accuracy of land cover maps remains a great uncertainty and mapping accuracy assessment is not well-documented. The objective of this paper is to examine the relationship between overall accuracy and the number of classification classes by conducting a literature review of land cover/land use studies. The results revealed a weak negative correlation between the map's accuracy and the number of classes. The paper suggests a decrease of 0.77% map's overall accuracy with respect to the increase of 1 land cover class. The average overall accuracy produced by 05 sensor types does not show the big difference. In addition, high spatial resolution sensor such as Airborne might not be always advantageous for producing high overall accuracy map since its accuracy depends on several factors including the number of land cover classes.

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  • Seika Tanji, Masaru Inatsu
    2019 Volume 15 Pages 32-36
    Published: 2019
    Released: February 13, 2019
    [Advance publication] Released: January 23, 2019
    JOURNALS FREE ACCESS

    Blowing snow potential is diagnosed for typical cases around Sapporo, Japan, as snow concentration and visibility based on dynamically downscaled data with 1-km resolution. The results are consistent with the blowing-snow records on time and place of traffic disruption, when the dynamical downscaling (DDS) reproduced wind speed well for a case. The diagnosis with mesoscale model analysis with 5-km resolution does not reproduce the blowing snow events in most area, however. Hence, the DDS potentially, not perfectly, adds the value to estimate blowing snow potential, despite a large scale-gap from an explicit representation of small-scale turbulence related to blowing snow. Sensitivity tests clarify that blowing snow requires strong wind and freezing temperature at the surface.

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  • Van Q. Doan, Hiroyuki Kusaka
    2019 Volume 15 Pages 37-40
    Published: 2019
    Released: February 19, 2019
    [Advance publication] Released: January 23, 2019
    JOURNALS FREE ACCESS

    This study introduces a new multiple-layer urban canopy model (MUCM) combined with a ray-tracing algorithm. In the model, we parameterize the urban morphology as an infinite array of identical three-dimensional buildings separated by roads. Heat exchanges are solved for each urban surface at each vertical layer. The ray-tracing scheme is used to explicitly calculate the view factors as well as both the sunlit and shadow fractions of the urban surfaces during the daytime. As a test, we show that this combined MUCM accurately models observations at Kugahara, Tokyo. Thus, the combined MUCM is a new tool for urban climate modelers to more realistically represent radiative processes on urban surfaces. In particular, it may contribute to our understanding of urban climate in the mega-cities of Asia, which generally have high-rise buildings that are more difficult to model with simpler radiative schemes.

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  • Koji Terasaki, Shunji Kotsuki, Takemasa Miyoshi
    2019 Volume 15 Pages 41-46
    Published: 2019
    Released: February 28, 2019
    [Advance publication] Released: January 31, 2019
    JOURNALS FREE ACCESS

    This study investigates the long-term stability of the global atmospheric data assimilation system, incorporating the Local Ensemble Transform Kalman Filter (LETKF) with the Nonhydrostatic ICosahedral Atmospheric Model (NICAM). The NICAM-LETKF system assimilates conventional observations, advanced microwave sounding unit–A (AMSU-A) radiances, and global satellite mapping of precipitation (GSMaP) data. The long-term stability of the data assimilation system can be investigated only by running an expensive long-term experiment. This study successfully performed a data assimilation experiment with more than 2 years of data, using the relaxation to prior spread (RTPS) method for covariance inflation. Analysis fields indicate a stable physical performance compared with the ERA-interim data for the entire experimental period.

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  • Wenkai Li, Shuzhen Hu, Zongmei Pan, Xiaoyun Su, Xinyue Luo, Yijuan Wan ...
    2019 Volume 15 Pages 47-51
    Published: 2019
    Released: February 28, 2019
    [Advance publication] Released: January 31, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    The apparent temperature (APT), or human-perceived temperature, is commonly defined as a function of the surface air temperature (SAT), vapour pressure (or humidity) and wind speed. This paper demonstrates that the APT over China, as revealed by daily station-observed data, has generally increased faster than the SAT during summertime in the past 50 years (1968-2017). The rate of increase in APT was significantly faster than that of SAT in 60.1% of stations, and the difference between the average China-wide APT and SAT was 0.11°C decade−1. This phenomenon is occurring nationwide, but it is more intense over western, north-eastern and eastern coastal China. The more rapid increasing trend in APT indicates that human beings actually experience surplus heat stress under a certain change in SAT, and the increased SAT explains 67.0% of the average APT warming for the country, contributing to the change in the base APT. Apart from the increasing SAT, a decrease in surface wind speed and an increase in surface vapour pressure have also been observed, contributing to 21.6% of the increase in APT and explaining the remaining 11.4%, respectively.

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  • Kei Kawai, Yuta Nishio, Kenji Kai, Jun Noda, Erdenebadrakh Munkhjargal ...
    2019 Volume 15 Pages 52-56
    Published: 2019
    Released: March 07, 2019
    [Advance publication] Released: February 01, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    Asian dust is transported over a long range via the mid-latitude westerlies when dust is lifted to the free troposphere over the source regions, whereas dust remaining in the atmospheric boundary layer is not transported far. In the Gobi Desert, a major source region of Asian dust, a ceilometer (compact lidar) monitors the vertical distribution of dust at Dalanzadgad, Mongolia. On 29-30 April 2015, the ceilometer observed a developed dust storm over the ground, followed by a dust layer within a height of 1.2-1.8 km. The dust storm had already developed in the upwind region before reaching Dalanzadgad. This feature was also shown in the ceilometer observation data. The dust layer remained at almost the same height for 12 h, because the dust became trapped within an inversion layer at a height of 1.2-1.5 km over cold air. This result suggests that the inversion layer prevented the dust from reaching the free troposphere, thereby restraining the long-range transport of the dust via the westerlies. This is the first paper that reports this type of vertical distribution of dust in the source region based on observation data.

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  • Shogo Sakai, Hironobu Iwabuchi, Feng Zhang
    2019 Volume 15 Pages 57-61
    Published: 2019
    Released: March 16, 2019
    [Advance publication] Released: February 19, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We have developed a rapid simplified algorithm to retrieve cloud optical thickness and cloud-top height from measurements of the infrared split-window bands of Himawari-8. The method is based on a rapid calculation model for clear-sky brightness temperatures and empirical equations for cloud, for which the coefficients are determined by a fit to a more rigorous radiative-transfer model. This method can be applied regardless of regions excluding the polar regions and season by taking into account the temperature, humidity, sea surface temperature, and surface emissivity. In this study, we have demonstrated that this method captures well the diurnal cycle of cloud amounts of different cloud types in the warm-pool region around Indonesia. With an accelerated retrieval process by a factor of around 1,000 compared with the the physics-based retrieval, our rapid cloud retrieval algorithm yielded cloud amounts that agree quantitatively with those from a more rigorous, physics-based cloud retrieval method.

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  • Hai Bui, Shigeo Yoden, Eriko Nishimoto
    2019 Volume 15 Pages 62-67
    Published: 2019
    Released: March 21, 2019
    [Advance publication] Released: February 25, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We present a three-dimensional minimal model that produces a self-sustained oscillation reminiscent of the quasi-biennial oscillation (QBO) in a radiative–moist convective quasi-equilibrium state. The computational domain is rectangular (640 km × 160 km) with doubly periodic boundary conditions. After initial transient time, an oscillation with a period of about 300 days emerges in the stratosphere, both in the domain-averaged zonal wind and meridional wind. A synchronization of the zonal and meridional winds is observed and is characterized as an anti-clockwise rotation of a skewed spiral feature with height in the mean horizontal wind vectors. The QBO-like wind oscillations penetrate into the troposphere. Modulation of tropospheric temperature anomalies and precipitation occurs with an irregular period of about 100 days, in which heavy precipitation is associated with positive temperature anomalies. The simulation reveals three types of precipitation patterns: isolated quasi-stationary type clusters, fast-moving back-building type and squall-line type patterns. The quasi-stationary type is newly identified in this three-dimensional model. Intermittent self-organization of convective systems into quasi-stationary type and transition back to the fast-moving back-building type or squall-line type are fundamental characteristics of self-aggregation in the three-dimensional model.

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  • Feng Zhang, Hang Ren, Lijuan Miao, Yadong Lei, Mingkeng Duan
    2019 Volume 15 Pages 68-74
    Published: 2019
    Released: March 27, 2019
    [Advance publication] Released: February 25, 2019
    JOURNALS FREE ACCESS

    As the earth's third pole, Qinghai-Tibet Plateau belongs to one of the most sensitive regions to climate change in the world. Based on the observed and the simulated daily precipitation from the Coupled Model Intercomparison Project Phase 5 (CMIP5), we evaluated the simulation performance of daily precipitation from selected CMIP5 models from 1975 to 2005 over the Qinghai-Tibet Plateau. We found that daily precipitation exhibited obvious long-range correlation characteristics using the detrended fluctuation analysis method. The scaling exponents of daily precipitation in summer and autumn are significantly larger than those in spring and winter. MIROC4H with the best performance can reproduce long-range correlation characteristic of daily precipitation series probably because of the higher resolution, which can capture small scale cloud convections. Besides there are seasonal differences in the simulation results among different regions of the Qinghai-Tibet Plateau, simulation effects of all climate models in summer and winter are better than those in spring and autumn. The performance of MIROC4H model works the best in spring. Overall, the scaling exponents of daily precipitation from BCC-CSM1-1-M, CMCC-CM and MIROC4H are close to the observations. CCSM4 and MIROC4H climate models could reproduce the internal dynamics characteristic of daily precipitation in autumn. But for winter, all climate models have exaggerated the scaling value in southeastern Qinghai-Tibet Plateau compared with the observed values.

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  • Kazuto Takemura, Akihiko Shimpo
    2019 Volume 15 Pages 75-79
    Published: 2019
    Released: April 06, 2019
    [Advance publication] Released: March 04, 2019
    JOURNALS FREE ACCESS

    Herein, (i) the remote influence of positive Indian Ocean Dipole (P-IOD) events in enhancing Tibetan High and (ii) its impact on the East Asian climate, from July to September, is analyzed based on composite analysis and linear baroclinic model experiment. In the equatorial Indian Ocean, convective activity enhances over the western part and suppresses over the eastern, which is associated with the zonal contrast of the sea surface temperature anomaly during P-IOD events. A lower-tropospheric clockwise circulation anomaly is evident from the eastern equatorial Indian Ocean where the suppressed convection is seen to the Indochina Peninsula. The streamlines arrive at the seas east of the Philippines, contributing to the enhancement of the monsoon trough. In the upper troposphere, crucial divergence anomaly over a wide area in the western North Pacific and the associated stronger-than-normal northward divergent winds toward East Asia cause strong northward negative-vorticity advection over the northern part of East Asia, contributing to the northeastward extension of the Tibetan High. This circulation anomaly contributes to both the significantly hot conditions in boreal summer and the late-summer heat over East Asia.

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  • Kengo Arai, Kazuaki Yasunaga
    2019 Volume 15 Pages 80-86
    Published: 2019
    Released: April 12, 2019
    [Advance publication] Released: March 26, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study examines dominant precipitation patterns during winter in the north-central region (Hokuriku District) of Japan, based on empirical orthogonal functions (EOFs) analysis. The pattern of the first leading component is similar to that of the mean precipitation, and the second leading component shows a dipole structure in which positive and negative regions are separated by the coast line. This dipole pattern across the coast line is robust regardless of data stratifications for the EOF calculation. Composites reveal that maritime and inland precipitation is relatively enhanced before and after the passage of a mid-level trough, respectively. In the former case, the temperature is higher and westerly or southwesterly wind prevails, while northwesterly wind dominates in the latter case. It is suggested that interactions between cold air over the land and warm air over the ocean are essentially important to the distinct precipitation patterns; offshore winds wedge the inland cold air under the maritime warm air, and intensifies the precipitation over the ocean. On the other hand, the northwesterly monsoonal flow pushes the maritime warm air onto the inland cold air, and more precipitation is brought about around the mountain range.

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  • Han Lin, Feng Zhang, Kun Wu, Jing Xu
    2019 Volume 15 Pages 87-93
    Published: 2019
    Released: May 14, 2019
    [Advance publication] Released: April 01, 2019
    JOURNALS FREE ACCESS

    Five δ-two-stream and δ-four-stream schemes are compared in solar spectra using the Rapid Radiative Transfer Model for General Circulation Models Applications (RRTMG). By calculating the flux and heating rate in various atmosphere, it is found that, in accuracy, the δ-four-stream schemes overwhelmingly outperform the δ-two-stream schemes. The precision of adding algorithm of the δ-four-stream spherical harmonic expansion (δ-4SDA) is comparable to that of adding algorithm of the δ-four-stream discrete ordinates method (δ-4DDA). Furthermore, the accuracy of the adding algorithm of δ-Eddington approximation (δ-2SDA) is close to that of δ-two-stream approximation with Practical Improved Flux Method (δ-PIFM), while adding algorithm of δ-two-stream discrete ordinates method (δ-2DDA) produces the poorest results among the five approximate schemes. For the RRTMG model with radiative transfer calculation, the computational time of δ-4SDA is about 1.5 times that of δ-two-stream schemes, and the computational time of δ-4SDA is about 88% that of δ-4DDA.

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  • Kenji Suzuki, Rimpei Kamamoto, Katsuhiro Nakagawa, Michinobu Nonaka, T ...
    2019 Volume 15 Pages 94-98
    Published: 2019
    Released: May 14, 2019
    [Advance publication] Released: April 10, 2019
    JOURNALS FREE ACCESS

    A field observation was carried out along the coast of the Japan Sea in the 2016-2017 and 2017-2018 winter seasons, using the Ground-based Particle Image and Mass Measurement System (G-PIMMS) to evaluate the Global Precipitation Measurement Mission (GPM) dual-frequency precipitation radar (DPR) precipitation type classification algorithm. The G-PIMMS was installed at Kanazawa University and Ishikawa Prefectural University, which are around 10 km apart from each other. The G-PIMMS observations showed that the major precipitation particle type (graupel or snowflake) was different in the precipitation types classified by the GPM DPR algorithm.

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  • Tomoe Nasuno
    2019 Volume 15 Pages 99-106
    Published: 2019
    Released: May 16, 2019
    [Advance publication] Released: April 23, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    Transport of moisture over the western Maritime Continent (MC) was examined using global cloud-system-resolving simulations for the Years of the Maritime Continent (YMC) field campaigns in 2015 and 2017, under peak El Niño and moderate La Niña conditions, respectively. We focused on the role of high- and low-frequency variability in the moistening over land and ocean, and their relationship with intraseasonal oscillation (ISO) events.

    The period-mean profiles indicate moistening by low-frequency upward motion in the deep troposphere and drying (moistening) in the lower (middle and upper) troposphere by high-frequency variability. The advection over ocean was greater in 2017 than in 2015, with the opposite occurring over land with smaller interannual differences. Over ocean, the roles of the high-frequency variability in the ISO life cycle, namely, the lower-to-middle-tropospheric moistening (enhanced upward transport of moisture) during the preconditioning (active) phases of the ISO, were common in both years, while over land, the high-frequency effects were nearly in phase (not correlated) with the ISO in the 2015 (2017) case. These results highlight clear land-ocean contrasts in the sensitivity of local convection to the background state and its link with the ISO life cycle.

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  • Masaya Nosaka, Hiroaki Kawase, Hidetaka Sasaki, Akihiko Murata
    2019 Volume 15 Pages 107-112
    Published: 2019
    Released: May 22, 2019
    [Advance publication] Released: April 24, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    High-frequency variations are excluded in the merged satellite and in-situ data global daily sea surface temperature (MGDSST) used in weather forecasting in Japan Meteorological Agency. We investigated the importance of temporal resolution on sea surface temperature (SST) when predicting winter precipitation using the Non-Hydrostatic Regional Climate Model. We used seven-day temporal smoothing to investigate the influence of temporal resolution on prediction. The Gaussian filter was used as spatial smoothing for comparison with the influence of spatial resolution. The influence of the temporal resolution of SST on monthly precipitation is smaller than that of spatial resolution. However, the influence of the temporal resolution on daily precipitation is comparable to that of spatial resolution. The temporal resolution of SST greatly affects precipitation, particularly in December, as the variations in SST are largest compared to the rest of the year. Furthermore, the winter monsoon promotes the effect of SST on winter precipitation. Our experiments using seven-day moving average smoothing indicates that the temporal resolution of the SST on precipitation become about 15 %/K under the winter monsoon.

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  • Van Q. Doan, Van Nguyen Dinh, Hiroyuki Kusaka, Thanh Cong, Ansar Khan, ...
    2019 Volume 15 Pages 113-118
    Published: 2019
    Released: May 30, 2019
    [Advance publication] Released: April 25, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study revealed great potential and shortcoming of offshore wind energy in Vietnam by numerical simulations with Weather Research and Forecasting (WRF) model at 10-km resolution for 10 years (2006-2015). The greatest energy potential was found in the offshore area of Phu Quy island (Binh Thuan province). The area, alone, can provide the 38.2 GW power generation capacity corresponding to the increasing renewable-energy demand by 2030 planned by the country. There is also a drawback of the wind resource, which is associated with strong multiple-scale temporal variabilities. The seasonal variability associated with monsoon onsets and daily variability associated with the wind diurnal cycles were found ranging 30-50%. Meanwhile, the inter-annual variability could reach up to 10%. These variabilities must be considered when designing wind farms and grids over the region. Additionally, due to the fact that the WRF model performed climatological features of the winds well against the observations, this results indicate that it can be useful tools for wind-power assessment as compared to other reanalysis or QuikSCAT data with coarser spatio-temporal resolutions.

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  • Hien Xuan Bui, Jia-Yuh Yu, Hsiao-Wei Liu, Chia-Ying Tu, Pin-Ging Chiu, ...
    2019 Volume 15 Pages 119-124
    Published: 2019
    Released: May 30, 2019
    [Advance publication] Released: May 01, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    While most studies have argued a slower increase of 1-3% K−1 of precipitation globally, others note that this is not necessarily the case from a regional perspective. In this study, we examine the convective structure changes over the equatorial Pacific with highly increased precipitation under global warming using simulations from the High Resolution Atmospheric Model (HiRAM). The moisture budget analysis shows that the precipitation increases must result from a significant enhancement of convection, with a minor modulation from the thermodynamic effect. Two different types of enhanced convection are identified. Over the mean ascending region, precipitation increases are associated with an enhancement of deep convection; while over the mean descending region, the precipitation increases are a result of enhanced shallow convection.

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  • Tetsuya Takemi
    2019 Volume 15 Pages 125-131
    Published: 2019
    Released: May 30, 2019
    [Advance publication] Released: May 14, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study investigated the impacts of global warming on extreme rainfall produced by a slow-moving typhoon by conducting pseudo-global warming (PGW) experiments. We examined Typhoon Talas (2011) that caused long-lasting heavy rainfall exceeding 2000 mm over the Kii Peninsula. The experiments successfully captured the track and translation speed of the actual typhoon, which enabled to quantitatively assess the climate change impacts. The PGW experiments indicated that the extreme rainfall is intensified in the future climates than in the present climate. Especially, the higher extremes of the accumulated rainfall are projected to be more severe in the future climate scenario. The analysis on the environmental factors showed that the cases with increased precipitable water lead to the increases in rainfall in future climates, despite the stabilized atmospheric conditions. Among the PGW experiments, the most increased amount of rainfall was found not to be produced by the most intensified typhoon.

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  • Akifumi Nishi, Hiroyuki Kusaka, Lidia Lazarova Vitanova, Yuma Imai
    2019 Volume 15 Pages 132-136
    Published: 2019
    Released: June 20, 2019
    [Advance publication] Released: May 27, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We quantitatively evaluated the contributions of foehn winds and the urban heat island (UHI) effect to an extreme high-temperature nocturnal event at Niigata city on 23-24 August 2018. During this event, southeasterly winds blew continually across the Niigata Plain and temperatures on the plain were higher than those in the windward region of the mountain range. Back-trajectory analysis and numerical simulations with and without topography showed that the southeasterly winds were foehn winds that caused precipitation and latent heating on the windward slope of the mountain range. The foehn winds and UHI contributed about 2.8°C and 1.9°C, respectively, to the extreme high-temperature of 31.0°C at 2100 JST in Niigata city. The combined impact of the foehn winds and the UHI at Niigata was about 4.0°C during the night. The contribution of the foehn winds was greater at around midnight, whereas that of the UHI was greater during the early night.

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  • Xinyue Wang, Hironobu Iwabuchi, Naoya Takahashi
    2019 Volume 15 Pages 137-142
    Published: 2019
    Released: June 27, 2019
    [Advance publication] Released: May 29, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    Using several cloud properties retrieved from the Himawari-8 satellite, combined with the best track storm center information, the temporal-spatial features of tropical cyclone (TC) diurnal pulses in 2015 Super Typhoon Atsani (T1516) are coherently depicted. To demonstrate the radially outward transition processes of the diurnal pulses from one cloud type to another, we divided high clouds into three types: opaque high cloud (OHC), cirrostratus (Cs), and cirrus (Ci). Two alternatively appeared peaks in cloud top height (CTH) within the storm central area and their corresponding outward pulses are identified. The first pulse covers a 24-hour period, it starts at ∼0500-0700 local solar time (LST), with a gradual transition from OHC to Cs, then ends in Ci at around 0400 LST. The second pulse lasts for half a day and limited within 1000 km from the storm center. When the first CTH pulse ends in OHC, Cs, and Ci, their cloud fractional coverage and the outward expansion of large cloud optical thickness also reach maximum accordingly.

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  • Hiroki Teramura, Tomonori Sato, Kenta Tamura
    2019 Volume 15 Pages 143-148
    Published: 2019
    Released: June 27, 2019
    [Advance publication] Released: May 31, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study investigated the impact of land surface heterogeneity on Mesoscale Convective System (MCS) initiations in East Asia, using geostationary satellite data during June–August from 1996 through 2018. The detected MCSs over land exhibited clear diurnal variation with the lowest existence frequency at 10:00 and highest initiation frequency during 12:00-17:00 local time. To quantify land surface heterogeneity, the spatial standard deviation of equivalent Black-Body Temperature (TBB) within a cloud-free 0.35° × 0.35° box (σLSTBB: Land Surface TBB) was computed for 10:00 each day. A comparison of the σLSTBB and MCS databases revealed that the probability of MCS initiations increased with increasing σLSTBB in East Mongolia while the probability was not sensitive to σLSTBB in East China. This indicated that MCSs tend to form over heterogeneous land surface conditions in the semiarid region. We found that the impact of land surface heterogeneity on MCS initiations was highest over flat terrain in East Mongolia, where the convection trigger due to topographically-induced circulation was absent. These results suggest that the impact of land surface heterogeneity on MCS initiations during the warm season varies with climate zones and terrain complexities in East Asia, with strongest impact in semiarid and flat regions.

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  • Akifumi Nishi, Hiroyuki Kusaka
    2019 Volume 15 Pages 149-153
    Published: 2019
    Released: July 17, 2019
    [Advance publication] Released: June 13, 2019
    JOURNALS FREE ACCESS

    This study revealed that the Karakkaze events accompanied by rising temperature are more frequent than those accompanied by dropping temperature. This finding contrasted with the general belief for many years that the Karakkaze is a bora-type local wind. By focusing on the temporal evolution of temperature and wind, we were able to characterize three types of Karakkazes as follows: the surface wind speed and temperature both increase in the morning and then decrease in the afternoon (type Foehn-D); during the night, the temperature increases or stops decreasing, and the surface wind speed increases (type Foehn-N); and in the morning, the temperature decreases or stops increasing, and the surface wind speed increases (type Bora). As a result, we found that among the 238 Karakkazes that we identified, 103 were type Foehn-D events, 56 were type Foehn-N events, and 79 were type Bora events.

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  • Daisuke Matsuoka, Shiori Sugimoto, Yujin Nakagawa, Shintaro Kawahara, ...
    2019 Volume 15 Pages 154-159
    Published: 2019
    Released: July 23, 2019
    [Advance publication] Released: June 28, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    In this study, a stationary front is automatically detected from weather data using a U-Net deep convolutional neural network. The U-Net trained the transformation process from single/multiple physical quantities of weather data to detect stationary fronts using a 10-year data set. As a result of applying the trained U-Net to a 1-year untrained data set, the proposed approach succeeded in detecting the approximate shape of seasonal fronts with the exception of typhoons. In addition, the wind velocity (zonal and meridional components), wind direction, horizontal temperature gradient at 1000 hPa, relative humidity at 925 hPa, and water vapor at 850 hPa yielded high detection performance. Because the shape of the front extracted from each physical quantity is occasionally different, it is important to comprehensively analyze the results to make a final determination.

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  • Akifumi Nishi, Hiroyuki Kusaka
    2019 Volume 15 Pages 160-165
    Published: 2019
    Released: August 21, 2019
    [Advance publication] Released: July 12, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    In the present study, we conducted dual-sonde observations and a numerical simulation when the “Karakkaze”, a local wind in Japan, blew. The result showed that the basic features of the Karakkaze coincide closely with the characteristics of convexity wind defined as “strong winds in the leeward region of a convex-shaped mountain range”.

    Firstly, we investigated the horizontal distribution of surface winds during the Karakkaze event on 24 January 2019. The results showed that the Karakkaze blows in the downwind plain of the convexity of the mountain range.

    Secondly, we compared the vertical distribution of the winds inside and outside the Karakkaze region, using the results of dual-sonde observations and a numerical simulation. Our results showed that strong winds blew from near ground level to a height of 1.8 km above mean sea level (AMSL) in the Karakkaze region. In contrast, weaker winds were observed and simulated outside the Karakkaze region. The reason of the weaker winds is that a hydraulic jump occurs on the slope of the mountain range and that the area outside the Karakkaze region is located in a more leeward direction than the hydraulic jump. These features closely match the characteristics of convexity winds.

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  • Minghao Yang, Ruiting Zuo, Xin Li, Liqiong Wang
    2019 Volume 15 Pages 166-171
    Published: 2019
    Released: August 21, 2019
    [Advance publication] Released: July 12, 2019
    JOURNALS FREE ACCESS

    The Qian atmospheric forcing dataset is used to drive version 4.5 of the Community Land Model (CLM4.5) in off-line simulation tests. Based on the Global Land Evaporation Amsterdam Model (GLEAM) data, we attempt to ameliorate the canopy interception parameterization scheme in CLM4.5 by improving the empirical parameter and the physical structure. Considering that different plant functional types (PFTs) have different capacities to intercept rainfall is denoted as SEN1, and accounting for the influence of wind speed on canopy interception on the basis of SEN1 is denoted as SEN2. SEN1 shows obvious improvement in the simulated evaporation of intercepted water from vegetation canopy (Ec), not only greatly reduces the positive bias of the model to simulate Ec, especially in the equatorial region, but also significantly reduces the root mean square error (RMSE). SEN2 further improves the simulation of Ec by lowering the RMSE and increasing consistency with GLEAM data. In addition, the percentages of Ec over total evapotranspiration in both SEN1 and SEN2 are more reasonable and much closer to GLEAM data than that in CLM4.5.

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  • Jianbo Yang, Min Shao, Qingeng Wang, Xu Yang
    2019 Volume 15 Pages 172-177
    Published: 2019
    Released: August 24, 2019
    [Advance publication] Released: July 23, 2019
    JOURNALS FREE ACCESS

    The relationships between the prediction of near-surface winds and the corresponding time of observations in eastern China were explored using the Advanced Weather Research and Forecasting (WRF) model and the three-dimensional variational (3D-Var) scheme in the gridpoint statistical interpolation (GSI) system. A series of one-month experiments was conducted in January 2018 with different time window configurations from 0.01 to 3.0 h. The relationship between the wind observation time and the model forecast was non-linear. An observational time closer to the initial time in the model usually have greater impact on the prediction of near-surface wind speeds. Observations in the 0.4-0.8 h time window associated with abnormally high with large near-surface wind speeds provide a negative impact. The predictions improved at a much smaller rate when the time window was increased from 0.8 to 3.0 h. No significant difference was seen as the time window increased in wind direction predictions, even with large wind increments. The optimum configuration of the time window in the GSI 3D-Var system for predicting near-surface winds should therefore be 0.2 or 0.4 h. A better understanding of the relationships between the observations and the predictions will help select more effective observations when using the 3D-Var scheme.

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  • Ryo Onishi, Daisuke Sugiyama, Keigo Matsuda
    2019 Volume 15 Pages 178-182
    Published: 2019
    Released: September 05, 2019
    [Advance publication] Released: July 26, 2019
    JOURNALS FREE ACCESS

    We propose a super-resolution (SR) simulation system that consists of a physics-based meteorological simulation and an SR method based on a deep convolutional neural network (CNN). The CNN is trained using pairs of high-resolution (HR) and low-resolution (LR) images created from meteorological simulation results for different resolutions so that it can map LR simulation images to HR ones. The proposed SR simulation system, which performs LR simulations, can provide HR prediction results in much shorter operating cycles than those required for corresponding HR simulation prediction system. We apply the SR simulation system to urban micrometeorology, which is strongly affected by buildings and human activity. Urban micrometeorology simulations that need to resolve urban buildings are computationally costly and thus cannot be used for operational real-time predictions even when run on supercomputers. We performed HR micrometeorology simulations on a supercomputer to obtain datasets for training the CNN in the SR method. It is shown that the proposed SR method can be used with a spatial scaling factor of 4 and that it outperforms conventional interpolation methods by a large margin. It is also shown that the proposed SR simulation system has the potential to be used for operational urban micrometeorology predictions.

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  • Shun-ichi I. Watanabe, Hiroyuki Tsujino, Akihiko Murata, Masayoshi Ish ...
    2019 Volume 15 Pages 183-188
    Published: 2019
    Released: September 05, 2019
    [Advance publication] Released: July 31, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We evaluated the impact of sea surface temperature (SST) improvement realized by increasing horizontal resolution of an ocean model on dynamical downscaling (DDS) over Japan, focusing on the effects of the Kuroshio on summer precipitation in Japan. Two sets of SSTs were simulated using a high-resolution North Pacific (NP) model and a low-resolution global (GLB) ocean model. Using these SSTs as the lower boundary conditions for the atmosphere, two DDS experiments were conducted (NP-run and GLB-run). In NP-run, summer precipitation increases over the Kuroshio and reduces over Pacific coastal areas of Japan compared with GLB-run. Due to weaker southerly winds north of the Kuroshio in NP-run, the water vapor flux transported to Japan is smaller than in GLB-run. Both the pressure adjustment and the vertical mixing mechanisms weaken the southerly winds, with the latter being slightly more effective. Increasing the horizontal resolution of the ocean model, so that the Kuroshio is more realistically reproduced, improves the accuracy of simulated precipitation over Japan.

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  • Jia Liu, Xiaofeng Xu, Xiangyang Luo
    2019 Volume 15 Pages 189-192
    Published: 2019
    Released: September 11, 2019
    [Advance publication] Released: August 05, 2019
    JOURNALS FREE ACCESS

    Accurate estimation of tropical cyclone (TC) intensity is of great significance for serious natural disasters. A new method is presented to estimate intensity of TC using satellite infrared data. Firstly, TC region is calculated according to the location of TC center. Secondly, 2D-PCA algorithm is used to extract feature of bright temperature image, and historical data of TC intensity is matched with the k-nearest neighbor algorithm. Thirdly, the matching results are analyzed and the intensity information of TC is estimated. In addition, a TC intensity database, which contains historical data during 2006-2010, is developed for estimation of TC intensity. Experiments show that the proposed method is efficient for real-time estimation of TC intensity, average error of estimation is lower than 15 hPa.

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  • Takenari Kinoshita, Koutarou Takaya, Toshiki Iwasaki
    2019 Volume 15 Pages 193-197
    Published: 2019
    Released: September 13, 2019
    [Advance publication] Released: August 06, 2019
    JOURNALS FREE ACCESS

    The mass-weighted isentropic zonal mean (Z-MIM) equations derived by T. Iwasaki are powerful tools for diagnosing meridional circulation and wave-mean interaction, especially for the lower boundary and unstable waves. Recently, some studies have extended the equations to three dimensions by using the time mean instead of the zonal mean. However, the relation between wave activity flux and residual mean flow (not mass-weighed mean flow) is unclear. In the present study, we derive the three-dimensional (3D) wave activity flux and residual mean flow for Rossby waves on the mass-weighted isentropic time mean equations. Next, we discuss the relation between the obtained formulae and 3D transformed Eulerian-mean (TEM) equations.

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  • Alessandro Damiani, Hitoshi Irie, Tamio Takamura, Rei Kudo, Pradeep Kh ...
    2019 Volume 15 Pages 198-204
    Published: 2019
    Released: September 27, 2019
    [Advance publication] Released: August 21, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We used observations recorded at Chiba University in November 2018 to examine the variability in cloud optical depth (COD) under overcast conditions. First, we conducted a careful evaluation of four COD datasets retrieved from three types of surface observations: i) zenith radiance recorded by two sky radiometers; ii) solar radiation data collected by a pyranometer; and iii) spatial distribution of radiance recorded using a sky camera system. Although the COD retrieved from the pyranometer (camera) slightly (moderately) overestimated the COD from zenith radiance, we found a satisfactory correlation among all surface estimates. This result suggests the efficacy of both pyranometer- and camera-based approaches and supports their broader use when dedicated cloud observations are not available. We then assessed satellite-based COD estimates retrieved from the recently launched Advanced Himawari Imager (AHI) aboard Himawari-8 (H-8) and Second-generation Global Imager (SGLI) on the Global Change Observation Mission for Climate (GCOM-C). Overall, we found good agreement between ground and satellite estimates; their correlation and root mean square error were virtually equivalent to values reported for co-located surface-based instruments. Nevertheless, the AHI-based COD was found to be slightly positively biased with respect to surface datasets.

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  • Hidekazu Matsueda, Rebecca R. Buchholz, Kentaro Ishijima, Helen M. Wor ...
    2019 Volume 15 Pages 205-210
    Published: 2019
    Released: September 27, 2019
    [Advance publication] Released: September 06, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    We analyzed temporal variations of carbon monoxide (CO) in the upper troposphere from 30°N to 30°S observed using instruments aboard commercial airliner flights between Japan and Australia over the period 1993-2016. Here we focused on the CO variations in the Southern Hemisphere (SH) that showed a unique seasonal cycle with an increased CO around October-November every year. The seasonal CO peaks in the SH showed significant interannual variability (IAV), and are notably enhanced in strong El Niño years, especially 1997. The CO enhancements are proportionally associated with CO emissions from Indonesian fires, when compared to the Global Fire Emissions Database (GFED). The IAV of the CO peak anomalies relative to the mean seasonal cycle was assessed by a statistical regression model that uses a combination of multiple climate indices and their interaction terms. We found that over 80% of the CO IAV observed in the upper troposphere could be explained by the model. The largest anomaly in 1997 showed a different CO-climate relationship than the other periods, which could be due to amplification during synchronized climate modes, or include additional influence from other factors such as human activities.

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  • Yan Nie, Lijuan Li, Yanli Tang, Bin Wang
    2019 Volume 15 Pages 211-215
    Published: 2019
    Released: October 29, 2019
    [Advance publication] Released: September 23, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    External forcings among the different phases of the Coupled Model Intercomparison Project (CMIP) vary considerably, but their impacts have not been extensively investigated yet. This study compares the impacts of CMIP5 and CMIP6 forcings on model stability and the 20th-century global warming and El-Niño Southern Oscillation (ENSO) based on the Pre-Industrial control (PI-control) and historical runs of the Flexible Global Ocean–Atmosphere–Land System Model: Grid-point Version 2 (FGOALS-g2). Results indicate that CMIP6 forcings result in a larger climate drift and a lower climatological global average surface temperature (GAST) than those of CMIP5 in PI-control runs. In historical runs, stronger 20th-century warming trends occur during the periods 1910-1940 and 1970-2005 using CMIP6 forcings, which are closer to the HadCRUT than those of the CMIP5 forcings simulation. A stronger spurious warming trend in the CMIP6 results in an evolution of GAST that is less consistent with the HadCRUT dataset than that in the CMIP5 during 1940-1970. Among all forcings, GHGs and aerosol forcings play the dominant roles in differences in GAST, particularly in the Northern Hemisphere. In both the PI-control and historical runs, a larger ENSO amplitude and smaller seasonality are simulated in CMIP6 than in CMIP5.

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  • Abd. Rahman As-syakur, Keiji Imaoka, Kakuji Ogawara, Manabu D. Yamanak ...
    2019 Volume 15 Pages 216-221
    Published: 2019
    Released: November 08, 2019
    [Advance publication] Released: September 24, 2019
    JOURNALS FREE ACCESS

    We analyzed 3-hourly Tropical Rainfall Measuring Mission multi-satellite analysis (TRMM 3B42) version-7 data for the 17-year period 1998-2014 to investigate seasonal and geographic characteristics of the diurnal rainfall cycle (DRC) over Sumatera, Indonesia. Dividing Sumatera into north, central, and south regions approximately perpendicular to the west coast, we point out for the first time early-afternoon initiation of daily rainfall not only in the Barisan Mountains but also in the east-coastal small islands (ECSIs) such as Bangka and Belitung. Westward and eastward migrations of rainfall areas from the Barisan Mountains are varied with seasons and regions, with the most remarkable being westward during September-October-November (SON) in the central region and the least remarkable occurring during June-July-August (JJA) in the southern region. In the central region, the DRC reaches a distance of ∼700 km off the west coast during SON and of only 200 km during March-April-May (MAM). The other westward migrations from the ECSIs in the central and southern regions (except for JJA) have been confirmed by 5-year hourly Multi-functional Transport Satellite-1R (MTSAT-1R) cloud-top data. The results shown in this paper suggest that the rainfall distribution with respect to coastal distance, varying geographically and seasonally.

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  • Kazuo Saito
    2019 Volume 15 Pages 222-227
    Published: 2019
    Released: November 12, 2019
    [Advance publication] Released: October 10, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    It is well known that northward winds are often observed at southern coastal areas of Japan when a developed tropical cyclone is located off the south coast of Japan. These northward winds have been frequently referred to the northward emission of warm and humid air from the typhoon which cause pre-typhoon rainfalls, but their mechanism has not been clarified. In this paper, we show that the northward wind can be explained by the ageostrophic wind components dynamically induced by acceleration vector round the tropical cyclone.

    On 7 October 2009, when a developed typhoon (T0918 Melor) approached Japan, distinct northward winds were observed at aerological observations over western Japan. Using numerical simulations with the Japan Meteorological Agency nonhydrostatic model, we reproduced the observed northward wind and their mechanism were examined by numerical experiments.

    The origin of the northward winds is explained by the ageostrophic winds dynamically induced by the acceleration vectors. When a typhoon approaches a baroclinic zone from south, northeastward ageostrophic winds are induced by southeastward acceleration vectors. Other possible causes (diabatic heating and orographic effect) are examined by sensitivity experiments. Diabatic heating by moist process acts to enhance the ageostrophic winds but the role is not primary. Orography has little effect on the observed ageostrophic wind.

    Non-axisymmetric features of the upper level divergence flow of a tropical cyclone near a baroclinic zone can also be elucidated by the similar mechanism of the ageostrophic winds.

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  • Hanako Y. Inoue, Kenichi Kusunoki, Toru Adachi, Chusei Fujiwara, Naoki ...
    2019 Volume 15 Pages 228-233
    Published: 2019
    Released: November 12, 2019
    [Advance publication] Released: October 18, 2019
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    The characteristics and finescale evolution of misovortices within a snowband were examined using low-level high-resolution single- and dual-Doppler radar analysis. From 02:00 to 06:00 JST on 17 January 2017, many misovortices developed within three snowbands in the Japan Sea coastal region. The vortices developed along the shear line between the offshore north-northwesterly and the coastal northeasterly. As discussed in several previous studies of misovortices along airmass boundaries, horizontal shearing instability was considered to be a possible mechanism responsible for misovortex formation. A detailed investigation was performed on the most distinct snowband and misovortices embedded within it. Dual-Doppler analysis revealed a detailed behavior of vortex during merger, such as the morphological change from quasi-circular to elliptical shape, and the counterclockwise rotation which caused high-amplitude inflection of the shear line in less than 10 minutes. During the decay stage, the vortices weakened along with weakening convergence. The results suggest that evolution of the misovortex appears to have been closely tied to the low-level convergence within the vortex.

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  • Kenichi Kusunoki, Ken-ichiro Arai, Hanako Y. Inoue, Chusei Fujiwara
    2019 Volume 15 Pages 234-237
    Published: 2019
    Released: November 15, 2019
    [Advance publication] Released: October 24, 2019
    JOURNALS FREE ACCESS

    On 11 December 2012, a wind gust caused an F0-intensity wind damage in the Shonai area, Yamagata Prefecture, Japan. This paper provides an overview of an anticyclonic misocyclone (i.e., anticyclonic circulation in the Doppler velocity) related to a wind gust from X-band Doppler radar data. The anticyclonic misocyclone was embedded within a cell with a spiral echo diameter of approximately 3-4 km. The misocyclone over the Sea of Japan moved southeastward at a speed of 11 m s−1, made landfall, and passed over the damaged area; this timing is consistent with the Japan Meteorological Agency (JMA) wind damage assessment. Over the damaged area, the diameter of the misocyclone in the Doppler velocity was estimated to be smaller than 893 m, and the peak tangential wind speed and the vorticity of the vortex were estimated to be at least 8 m s−1 and −3.6 × 10−2 sec−1, respectively. This study discusses various possible explanations for the relationship between the misocyclone and wind gust and provides a first overview of a wintertime anticyclonic misocyclone associated with a surface wind gust on the coast of the Sea of Japan and may provide useful insights to the understanding of wintertime vortices.

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  • Kazuaki Yasunaga, Atsushi Hamada, Kazuaki Nishii
    2019 Volume 15 Pages 238-243
    Published: 2019
    Released: November 30, 2019
    [Advance publication] Released: November 06, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study examines the factors responsible for the long-term changes of winter monsoonal flow around Japan in association with increasing precipitation trends in December along the coastal areas of Honshu (the main island of Japan) facing the Sea of Japan. The precipitation around the tropical eastern Indian Ocean and maritime continent has significantly increased in recent years. Thus, a packet of the stationary Rossby wave associated with the anomalous heating deflects the subtropical jet to the south over the eastern edge of the Eurasian continent. The deflection of the jet gives favorable conditions for the development of a low pressure trough in the lower level on the eastern side, leading to the formation of negative height anomalies near the surface around Japan.

    Although tropical precipitation also increases in November and January, the anomalous heating induces negative height anomalies and cyclonic circulations over the inland region of China and eastern offshore region of Japan (to the further west and east in comparison with those in December) in these months. As a result, monsoonal flow around Japan (and precipitation along the coastal areas of the Sea of Japan) shows no long-term trends in November or January.

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  • Sachie Kanada, Hidenori Aiki, Kazuhisa Tsuboki, Izuru Takayabu
    2019 Volume 15 Pages 244-249
    Published: 2019
    Released: December 05, 2019
    [Advance publication] Released: November 07, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    From 16 to 23 August 2016, typhoons T1607, T1609, and T1611 hit eastern Hokkaido in northern Japan and caused heavy rainfall that resulted in severe disasters. To understand future changes in typhoon-related precipitation (TRP) in midlatitude regions, climate change experiments on these three typhoons were conducted using a high-resolution three-dimensional atmosphere–ocean coupled regional model in current and pseudo-global warming (PGW) climates. All PGW simulations projected decreases in precipitation frequency with an increased frequency of strong TRP and decreased frequency of weak TRP in eastern Hokkaido. In the current climate, snow-dominant precipitation systems start to cause precipitation in eastern Hokkaido about 24 hours before landfall. In the PGW climate, increases in convective available potential energy (CAPE) developed tall and intense updrafts and the snow-dominant precipitation systems turned to have more convective property with less snow mixing ratio (QS). Decreased QS reduced precipitation area, although strong precipitation increased or remained almost the same. Only TRP of T1607 increased the amounts before landfall. In contrast, all typhoons projected to increase TRP amount associated with landfall, because in addition to increased CAPE, the PGW typhoon and thereby its circulations intensified, and a large amount of rain was produced in the core region.

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  • Junya Fukuda, Munehiko Yamaguchi
    2019 Volume 15 Pages 250-256
    Published: 2019
    Released: December 26, 2019
    [Advance publication] Released: November 18, 2019
    JOURNALS FREE ACCESS

    The effectiveness of multiple ensembles to determine 70% probability-circle radii of operational tropical cyclone (TC) track forecasts in the Japan Meteorological Agency (JMA) is investigated. The ensembles used in this study are global ensembles from JMA, the European Centre for Medium-Range Weather Forecasts (ECMWF), the National Centers for Environmental Prediction (NCEP) and the Met Office in the United Kingdom (UKMO). The verification for all TCs from 2016 to 2018 reveals that the multiple ensemble-based method has stronger correlation with operational TC track forecast errors and the clearer degree of separation among confidence levels derived from the ensemble spreads than the conventional statistical and single ensemble-based methods. It indicates that the multiple ensemble method provides situation-dependent forecast uncertainty most appropriately. As the effectiveness of the multiple ensemble method has been confirmed, JMA started to operate the multiple ensemble-based 70% probability-circle radii for its operational TC track forecasts for all forecast times up to 120 hours in June 2019. The radii are based solely on confidence levels derived from cumulative ensemble spreads of the multiple ensemble from the 4 centers. This is a good example of successful research to operation transfer of The International Grand Global Ensemble (TIGGE) project.

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  • Nobuo Sugimoto, Yoshitaka Jin, Atsushi Shimizu, Tomoaki Nishizawa, Kei ...
    2019 Volume 15 Pages 257-261
    Published: 2019
    Released: December 26, 2019
    [Advance publication] Released: November 26, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    Mineral dust transported from Africa and Middle East was observed with the Asian Dust and aerosol lidar observation Network (AD-Net). In March 2018, the dense Sahara dust, reported by mass media as that snow in Sochi, Russia stained into orange, was transported to Sapporo in 4 days from Sochi and observed by the lidar. In April 2015, dust from Middle East was transported to Nagasaki passing across the Taklamakan desert. Dust source areas and transport paths were studied with the global aerosol transport model MASINGAR mk-2 separately calculated for different dust sources regions. The results showed that dust from Sahara and Middle East was transported to East Asia and sometimes mixed with dust from the Gobi desert and the Taklamakan desert. The analysis of recent AD-Net data after 2015 showed such long-range transport cases were observed every year in March or April. The transport path often led over the Caspian Sea, Kazakhstan, and Russia. Sahara dust transported north and reached around the Black Sea was transported long range by strong westerly in springtime.

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  • Tomomichi Ogata, Hidenori Aiki
    2019 Volume 15 Pages 262-267
    Published: 2019
    Released: December 27, 2019
    [Advance publication] Released: December 02, 2019
    JOURNALS FREE ACCESS
    Supplementary material

    This study makes a first attempt to apply the diagnostic scheme of Aiki et al. (2017) to the output of an ocean general circulation model (OGCM), in order to investigate the basin-wide pathway of equatorial and mid-latitude wave energy associated with intraseasonal variability in the Indian Ocean. The vertical mode decomposition shows that 90-day variability of the second baroclinic mode is dominant in a realistic OGCM experiment. For 90-day equatorial Kelvin wave (KW) and Rossby wave (RW), energy input by wind stress appears in the eastern equatorial Indian Ocean that is then transferred eastward by KWs along the eastern equatorial waveguide (while westward as RW off equator). For 30-day Mixed-Rossby Gravity waves (MRG), wave energy is transferred eastward while wave phase propagates westward that is consistent with the dispersion relationship of low-frequency MRG. The new diagnostic scheme is able to show, particularly for 30-day MRG, eastward energy fluxes along the equatorial waveguide, while the other schemes in previous studies (e.g. pressure flux, quasi-geostrophic flux) cannot show the direction of the group velocity of equatorial waves.

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